Standard wifi encryption you'll run into nowadays is WPA2. It works by performing an authentication handshake in which key hashes and things are exchanged as part of a client signing up to the network. The pwnagotchi works by seeking out nearby wifi networks; It then listens for their clients, kicks their clients off the network, and then listens for the authentication handshake when the client attempts to reconnect. Individually, it's a reasonably quick process that the client user never even notices. The handshake that the pwnagotchi acquires, if short or simple enough, can then be used with a hash cracker to find the wifi network's passcode.

A standard pwnagotchi uses a raspberry pi zero w which is like $15 bucks and while it works, its wifi isn't the greatest for long range sniffing. But if you're walking around for a while in an office building , neighborhood, or a more thought out location you can usually find yourself with enough hashes to at least take a stab cracking their wifi passcode. For free wifi or more creative endeavors.

It's a nice and easy introduction to wifi hacking concepts, if that's your thing.